Method of making intermediate shell construction for silencer or muffler



March 29, 1966 J. H. sELlG METHOD OF MAKING INTERMEDIATE SHELLCONSTRUCTION FOR SILENCER OR MUFFLER 4 Sheets-Sheet 2 Filed June l5,1962 IN VENTOR: JAMES H. SEL la.

March 29, 1966 J, H, SELIG 3,242,558

METHOD OF MAKING INTERMEDIATE SHELL CONSTRUCTION FOR SILENOER OR MUFFLERFiled June 1.3, 1962 4 Sheets-Sheet 5 IN VEN TOR: JAMES H. SEL m.

TIE -7- MQW March 29, 1966 J. H. SELIG METHOD OF MAKING INTERMEDIATESHELL CONSTRUCTION FOR SILENCER OR MUFFLER Filed June 13, 1962 4Sheets-Sheet 4, v

United States Patent O METHOD OF MAKING INTERMEDIATE SHELL CONSTRUCTIONFOR SILENCER OR MUFFLER James H. Selig, Grand Haven, Mich., assignor toOldberg Manufacturing Company, Grand Haven, Mich., a corporation ofMichigan Filed June 13, 1962, Ser. No. 202,143 7 Claims. (Cl. 29-157)This invention relates t-o a method of making an intermediate shellconstruction for a mufller or silencer of la character particularlyadaptable for silencing or attenuating sound waves entrained in exhaustgas streams of internal combustible engines and more especially to anintermediate shell and gas pass-age tube construction or unit for use ina mufer or silencer.

It has been a general practice in conventional types of muffler orsilencer to provide one or more gas passage tubes wherein the gaspassage tube is surrounded or embraced by lan imperforatecylindrically-shaped shell, termed an intermediate shell, for thepur-pose of providing s-ound attenuating chambers or compartments forattenuating or d-amping sound waves of comparatively high frequencies inan exhaust gas stream. A plurality of such chambers is usually providedbetween the intermediate shell and the gas passage tube wall by aplurality of annular rings or partition members spaced lengthwise of theshell, the space between each pa-ir of `annular members denng a highfrequency sound attenuating chamber.

Communication between the gas passage tube and adjacent high frequencysound attenuating chambers is attained through a comparatively largenumber of small openings in the gas passage tube wall in order toattenuate high frequency sound waves. Intermediate shell and gas passagetube constructions of this character have been expensive to produce dueto the number of rings required and the diiculties of spacing the ringsto secure sound. attenuating chambers of proper lengths. It has been ausual practice to weld the annular members or rings to the gas passagetube and then insert the assemblage of tube and rings within -anintermedia-te shell. In some instances, annular anges -on the rings arewelded to the intermediate shell. In constructions where the annularmembers are not securely held in position, vibration and varying gaspressures may cause noise.

The present invention embra-ces a novel method of assembling a gaspassage tube member and intermediate shell member construction for amuiiler wherein partition means between the tube member and the shellmember are integrally formed on one of said members thereby eliminatingthe use of annular members between the gas passage member and the'intermediate shell member.

Another object of the invention `resides in a method of forming`transversely extending partition portions from one of said members bydistorting the metal of the member in a manner whereby =a plurality ofannular chambers of `desired length are formed between the members bythe integral partition portions.

Another object of the invention resides in the method of fashioning aperforated gas passage tube and a surrounding shell to form a pluralityof high frequency sound attenuating chambers wherein transverselyextending integral portions of the shell member are formed by a 4seriesof progressive steps of distorting the metal of the shell to formannular partitions or walls which engage the gas passage tube to defineannularly-shaped sound attenuating chambers.

Another object of the invention resides in a method `of forming andassembling a gas passage tube and intermediate shell tube unit whereinspaced circular regions of the intermediate shell tube are distorted andforced inwardly in engagement with the gas passage tube disposed intelescoped relation with the intermediate shell tube.

Another object of the invention is the provision of a method of formingtransversely extending integral circular flanges on a metal tubeinvolving the steps of `distorting the metal of the tube laterally bytransversely applied forces and subsequently applying pressurelengthwise of the tube to progressively further distort the metaltransversely and compress the distorted metal upon itself to form apartition substantially equal to twice the wall thickness yof the tube.

Another object of the invention resides in a method of form-ing anintermedi-ate shell unit for a mufer construction wherein portions ofthe intermediate shell wall are processed in a manner wherebytransversely exten-ding portions are progressively formed by pressurelapplied lengthwise of the shell.

Further objects and `advantages are within the scope of this inventionsuch as relate to the arrangement, operation and function of the relatedelements of the structure, to various details of construction and tocombinations of parts, elements per se, and to econ-omies of manufactureand numerous other features as will be apparent from a consideration ofthe specification and drawing of a form of the invention, which may bepreferred, in which:

FIGURE 1 is Ia longitudinal sectional view of Ia sound attenuatingmuffler embodying a form of intermediate shell and gas passage tubeconstruction of the invention;

FIGURE 2 is a transverse sectional view taken substantially on the line2-2 of FIGURE l;

FIGURE -3 is an elevational View of an intermedi-ate shell illustratingone of the method steps in fashioning the shell and gas passage units;

FIGURE 4 is a View illustrating an assembly of gas passage tube memberand intermediate shell member preparatory to `a subsequent step 'in themeth-od of forming the unit;

FIGURE 5 is a view similar to FIGURE 4 illustrating the step in themethod of completing the inter-mediate shell and gas passage unit;

FIGURE 6 is an enlarged fragmentary sectional view illustrating thepartitions formed on the intermediate shell defining the high frequencysound attenuating chambers in the unit construction;

FIGURE 7 is a transverse sectional View taken substantially on the line7 7 of FIGURE 6;

FIGURE 8 is a semi-schematic view illustrating a method of deepening the-grooves in the intermediate shell in a form of construction wherein thegas passage tube is of reduced diameter;

FIGURE 9 is a fragmentary detail view illustrating the configuration ofa groove in an intermediate shell upon completion of the method stepshown in FIGURE 8;

FIGURE 10 is a view showing a modied method of providing inwardlyextending partitions on the intermediate shell;

FIGURE 1l is a transverse sectional view taken substantially on the line11-11 of FIGURE l0;

FIGURE l2 is a View similar to FIGURE l0 showing a method step offorcing the partition portion inwardly into engagement with the gaspassage tube, and

FIGURE 13 is a sectional view illustrating a method of formingtransversely extending partitions on the gas passage tube.

While the unit construction and method of making the same haveparticular utility as a sound attenuating component in a silencer ormuiiler for attenuating sound waves entrained in exhaust gas streamsfrom internal combustion engines, it is to be understood that the methodof the invention of assembling cylindrically-shaped members may beemployed wherever the invention may be found to have utility.

One form of sound attenuating unit of the invention is illustrated inFIGURES 1 and 2 embodied in a muffler or silencer for use with anexhaust gas stream of an internal combustion engine. Referring toFIGURES 1 and 2, the muffler is inclusive of a main or outer shell,casing or housing 12 which, as shown in FIGURE 2, is of generally ovalshape. The muffler may be of other shape if desired. The shell or casing12 illustrated is of the double wall type having an outer layer of metal14 and an inner layer of metal 15 which are slightlyseparated to providea space 17 to reduce shell noise.

In certain installations it may be desirable to fill the space 17 withasbestos, mineral fibers or other high temperature resistant insulation.The shell or casing construction is provided with end walls, heads orclosures 18 and 19, each of the heads or closures being formed with aperipheral flange configuration 20 of generally U-shaped cross-sectionproviding a peripheral recess or groove which receives the mating orcontiguous end regions of the shell walls 14 and 15 in the manner shownin FIGURE 1.

The flanges 22 and 23 of the U-sha-ped configuration 20 may be rolled orcrimped into engagement with the vends of the shell walls 14 and 15 toform a huid-tight joint. The end wall 18 at the inlet end of the muffleris fashioned with an opening defined by a circular ange 24, the openingaccommodating a coupling sleeve or tubular tting'26 which is preferablywelded or otherwise secured to the flange 24.

The portion of the coupling sleeve exteriorly of the end head 18 isarranged to accommodate an exhaust inlet tube or exhaust pipe 28 adaptedto convey exhaust gases from an internal combustion engine into themuffler construction.

v The end head 19 at the exhaust outlet end of the muier is providedwith an opening defined by a circular flange 30 which accommodates acoupling sleeve or tubular fitting 31 welded or otherwise secured to theflange 30. The coupling 31 is adapted to be connected with a tailpipe(not shown) or other'tubular means for conveying away exhaust gases fromthe mufer.

Disposed within the muffler housing 12 are transversely spacedpartitions or headers 34, 35 and 36, the headers or partitions beingprovided with openings to receive gas passage tubes 38 and 40, the tube40 being a gas outlet tube connected with the outlet coupling 31, asshown in FIGURE 1. One or more of the headers may be provided withopenings 42, shown in FIGURE 2, to facilitate passage of gas through themuflier in addition to the tubes 38 and 40.

The muier shown in FIGURES 1 and 2 embodies a gas passage and soundattenuating unit construction 44 of the invention. The construction 44includes a tubular member 46, herein referred to as an intermediateshell, and a gas passage tube 48 of lesser diameter than theintermediate shell 46 arranged in telescoped relation therewith. In theembodiment illustrated, the inlet end of tube 48 is in telescopingrelation with the inlet fitting 26 and `forms a gas inlet passage tubefor conveying exhaust gases into the muffler through substantially thelength thereof.

The peripheral wall of the gas passage tube or member 48 is providedwith a comparatively large number of small openings or orifices 50.

The intermediate shell or member 46 is integrally formed with interiorlyextending portions 52, 54, 56 and 58 which engage the exterior surfaceof the gas passage tube or member 48 and provide therewith annularlyshaped high frequency sound wave attenuating chambers 62, 64 and 66. Theopenings 50, in the Wall of the gas passage tube 48, provide acousticcouplings with the chambers 62, 64 and 66 for attenuating sound waves ofcomparatively high frequency. The method of forming the soundattenuating unit 44 will be hereinafter described in detail.

The gas passage tubes 38 and 40 may also be perforated or fashioned withsmall openings in the walls thereof in various areas, if desired, `forgas transfer purposes as well 4 as sound attenuating purposes. Theheader or partition 34 forms with the inlet head 18 a chamber 70 whichis 1n communication with the gas passage tubes 38 and 40. The

end head 19 forms with the header or partition 36 a Y chamber 72 whichis in communication with the opposite ends of the gas passage tubes 38and 48. The chambers 70 and 72 provide for the transverse flow ofexhaust gases and form resonance chambers for attenuating low frequencysound waves.

In the arrangement shown in FIGURES 1 and 2, the exhaust gas stream froman internal combustion engine enters the inlet fitting 26 and gaspassage tube 48 from the gas conveying exhaust pipe 28.

The gases move through the gas passage tube 48 into the gas transferchamber 72 thence in retroverted directions through the gas passage tube38 and the gas transfer chamber 70 into the exhaust outlet tube 40 whichconveys the gases away from the muflier. High frequency sound Waves areattenuated in the sound attenuating chambers 62, 64 and 66 through theacoustic couplings provided by the openings 50.

The invention includes a novel method of forming the gas passage andsound attenuating unit 44 comprising the intermediate shell 46 and thegas passage tube 48. In the method of the invention, the partitions orbaliies 52, 54, 56 and 58 are integrally fashioned on the intermediateshell 46 or in the alternative as hereinafter described, on the gaspassage tube. The method involves the processing or distortion ofregions of the metal of the intermediate shell or tube 46 to form theintegral transversely extending partitions.

Referring to FIGURE 3, there is illustrated a step in the method ofprocessing the metal of the wall of the intermediate shell or tube 46 informing the baffles or partitions. The tube is mounted upon a rotatablesupport (not shown). The tube is rotated and the wall of the tubeengaged by a suitable forming or grooving roll or wheel 74 journaled ona pin 75 carried by a member 76. In order to form a groove in the tubewall, the grooving or forming roll 74 is progressively advanced towardthe tube in a direction normal to the axis 'of the tube 46 to form agroove or circular depression bounded by portions 78 and 79.

In order to stabilize the thrust of the forming roll 74 against thetube, an abutment roller 82 journally supported on a member 84 isengaged with the peripheral surface of the tube 46 at a regionpreferably diametrically opposite to grooving roll 74 in the mannershown in FIGURE 3. FIGURE 3 illustrates four grooves formed in the tube46, the forming roll 74 being illustrated in the position of completingthe fourth groove. In the method of forming the grooves as abovedescribed, each of the grooves is formed individually and in succession.When the metal is distorted in forming a groove, the over-all length ofthe tube 46 is reduced to provide the metal for the grooves. Throughthis method of progressively and successively forming each groove, thethickness of the metal in the grooves is maintained substantially thesame as the thickness of the portions of the tube wall 46 between thepairs of grooves so that there is no appreciable reduction in the-strength of the metal at the regions of the grooves.

The grooves are designated 51, 53, 55 and 57 in FIG- URE 3. Inprocessing the intermediate shell member 46, the groove 51 is of thegreatest depth. The grooves 53, 55 and 57 are of progressively lesserdepth although the difference between the depth of adjacent grooves maybe only a few thousandths of an inch. The reason for this differentialin depth of grooving will be hereinafter explained. Further steps in themethod of forming the sound attenuating unit 44 are illustrated inFIGURES 4 and 5.

After the formation of the grooves in the manner illustrated in FIGURE3, the perforated gas passage tube 48 is inserted or telescoped withinthe grooved walled intermediate shell 46 and the assemblymounted invertical position upon a supporting footing or block 86, as shown inFIGURE 4. The block v86 is provided with an annular upwardly projectingridge 88 which extends between the end regions of the tube 46 and thegas passage tube 48. The block 86 is provided with a horizontal ledge 90which is engaged by the -lower edge of the intermediate shell or tube46.

The block 86 is provided with a bore to slidably, yet snugly,accommodate the end region 91 of the gas passage tube 48, the end of thetube engaging or abutting the bottom wall 92 of the bore formed in theblock 86. Arranged above the upper end of the assembly is a movable head94 of a press or other means for exerting downwardly acting pressure.Secured to the press head 94 is an adapter or fitting 96 fashioned witha counterbore 97 accommodating the upper end region of the intermediateshell or tube 46.

The counterbore 97 terminates in a circular ledge 98 which is adapted toengage the upper end of the tube 46 as shown in FIGURE 4. The adapter 96is provided with a central bore 100 to accommodate the upper end regionof the gas passage tube 48. It should be noted that the wall definingthe central bore or chamber 100 is slightly tapered or converged in adirection as shown in FIGURE 4 to effect a centering of the gas passagetube 48 during further processing of the shell 46 in forming thelaterally extending partitions.

Surrounding the intermediate shell or tube 46 at the region of eachgroove is a pair of semi-circularly-shaped members 102 which engage theexterior wall of the tube 46 and provide an anuularly shaped means toconfine the metal of the tube wall 46 at the regions of the groovesduring further processing. FIGURE 5 illustrates the position of theassembly shown in FIGURE 4 at the cornpletion of a downward stroke ofthe press head or platen 94 which operation completes the formation ofthe partitions 52, 54, 56 and 58.

With the components in the relation shown in FIG- URE 4 and theconfining guide grips or members 102 in engagement with the exteriorsurface of the tube 46, downward movement of the press head 94 performsseveral steps in sequence. As the groove 51 at the lower end of theassembly shown in FIGURES 4 and 5, is the deepest of the four grooves,the downward pressure exerted by the press head 94 through the adapteror fitting 96 upon the upper end -of the tube 46 collapses the portions78 and 79 defining the groove 51 to the position shown in FIGURE 5forming the partition 52 comprising two contiguous thicknesses of themetal which previously defined the groove 51.

At the same time the collapsing of the metal occurs, the bight portionof the groove which, as shown in FIG- URE 4, was slightly spaced fromthe exterior wall surface of the tube 48, is forced into engagingrelation with the gas passage tube 48 under the pressure collapsing thewalls defining the grooves 51.

At the completion ofthe collapsing of the walls defining the lowergroove 51, solid resistance to further collapsing of the tube wall isobviated by confining dies or members 102 so that further downwardpressure of the press head 94 collapses the walls 78 and 79 defining thegroove 53, such collapsing forming the dual layered partition 54.

The same collapsing action successively takes place with respect to themetal defining the grooves 55 and 57 to form the integral partitions 56and 58. The progressive formation of the partitions by sequentialcollapsing of the walls of the grooves beginning at the bottom of theassembly occurs by reason of the diderence in depth of the successivegrooves.

The progressive collapsing is assured because the resistance tocollapsing of the metal regions defining the groove is dependent in ameasure upon the depth of the groove. The confining members 102surrounding the regions ofthe grooves prevent the metal of the tube orshell 46 from movlng outwardly during the collapsing step so that thelmetal defining the. grooves is..necessarily directed inwardly to effecta tight engagement of the metal forming the partitions with the exteriorsurface of the gas passage tube 48. A partial section of the finishedproduct or unit 46 is shown in FIGURE 6.

It should be noted that by reason of the successive collapsing of theportions 78 and 79 of each .groove in the tube wall 46, the length lofthe tube 46 in the finished unit is the lesser length than theuncollapsed tube shown in FIGURE 4.

Due to the progressive downward .movement of the metal or tube 46 incollapsing the successive portions to form the partitions, the downwardmovement of the distorted metal of the tube 46 may provide a partitionwhich is in a slightly canted position as shown in FIGURE 6, but theinterior circular surfaces of the .partitions are in engagement with thegas passage tube 48 `and thereby form the chambers 62, 64 and 66.

As will be seen from FIGURE 6, a sound attenuating and gas passage unitis provided wherein the high frequency sound attenuating chambers arefashioned or defined by inwardly extending circular partitions which areintegral with the tube 46, thus eliminating the use of severalindependent annular members between the intermediate shell and the gaspassage tube to form sound attenuating chambers. The method isparticularly advantageous in that it enables the accurate location orpositioning of the partitions lengthwise of the intermediate shell ortube 46.

Furthermore there is no possibility of looseness or lost motion betweenthe partitions and the gas passage tube 48 because the collapsing stepforces the inner circular edge regions defining the partitions into snugengagement with the gas passage tube 48 as shown in FIGURES 5 and 6.From the foregoing explanation of the method of forming the unit 44, thepartitions 52, 54, 56 and 58 define the annularly-shaped confined zonesor high frequency sound wave attenuating chambers 62, 64 and 66.

The completed sound attenuating unit comprising the intermediate shell46, the perforated gas passage tube 48 and the partition construction isthus completed and is assembled in the mufiier construction as shown inFIG- URE l. As the partitions defining the high frequency sound waveattenuating chambers are formed as integral components of theintermediate shell construction 46, the complete unit is formed of onlytwo components Viz. the intermediate shell 46 and the perforated gaspassage tube 48.

The foregoing described method steps are employed in fashioningintermediate shell units where the inside diameter of the outer shell 46is approximately 3A of an inch greater in diameter than the insidediameter of the gas passage tube 48. FIGURES 6 `and 7 are illustrativeof a completed unit wherein the intermediate shell or tube 46 is of adiameter of about 21/2 inches .and the gas passage tube 48 of a diameterof about 1% inches.

The method may be utilized to form partitions between an intermediateshell and a gas passage tube by employing `an additional method stepwhere the difference between the diameter of the intermediate shell andthat of the gas passage tube exceeds approximately 3A of an inch. FIG-URES 8 and 9 are illustrative of an additional step in fabric-ating anintermediate shell unit with a gas passage tube of reduced diameter ofapproximately 11/2 inches. In fashioning this form of construction, thesteps of the method illustrated in FIGURE 3 are substantially duplicatedin forming the grooves 108 i-n the intermediate shell or tube 110, aportion of the tube being shown in FIG- URE 8.

In order to exercise control of the metal of the shell at the regions ofthe grooves in forming the partitions, the metal at the region of thegrooves is distorted inwardly for a greater distance than the depth ofthe grooves formed 7 by the method step illustrated in FIGURE 3 `andhereinbefore described. After the grooves 108 are formed in the wall oftube 110in Vthe`rnanneshown'inlIGURE Y3, the bight portion of eachgroove is deepened by a suitable tool 112 shovm in FIGURE 8.

The tool 112 comprises a body 114 provided with the projection 116 whichis comparatively thin, as illustrated in FIGURE 8, and having a roundedend 118 engageable with the metal in the base or bight of a groove. Thetube 110 is rotated `about its longitudinal axis and the tool 112progressively moved into a groove in a direction normal to the axis ofthe tube to force the projection 116 toward the axis of the tube tothereby deepen the groove to approximately the configuration illustratedin FIGURE 9.

The action of forcing the tool projection 116 toward the axis of thetube while the tube is rotating effects a further distortion of themetal whereby the walls 120 and 122 defining the groove are brought morenearly into close parallel relation and simultaneously increasing thedepth of Vthe groove in the tube. In assembling a gas passage tube withthe construction shown in FIGURE 9, the

method illustrated in FIGURES 4 and 5 is employed to,

collapse the tube lengthwise to form the partitions.

Thus, after the tool 116 has been employed to deepen the grooves in theshell or tube 110, the gas passage tube 124, shown in FIGURES l yand ll,is inserted in the intermediate shell, and the walls 120 and 122 of eachgroove are brought together by the collapsing action by downwardmovement of the press head 94, shown in FIGURE 5, whereby the parallelwalls 120 and 122 of each groove are brought into contiguous relation toform the partitions 130, as shown in FIGURE 10.

During the endwise collapsing of the intermediate shell 110, the regionsof metal adjacent each of the grooves may be confined by matingsemicircular confining dies 126 so that during collapsing, the metal atthe region of the grooves is forced inwardly toward the gas passage tube124. In order to effect progressive closing or collapsing of the groovesin the final step of fabricating the partitions, it is preferable thatthe tool 116 be moved inwardly a greater distance in each successivegroove so that the grooves fro-m one end of the tube to the other areprogressively deeper.

Through this method, the wall regions defining the several ygrooves areprogressively collapsed by pressure on the end of the intermediate shellor outer tube in the manner illustrated in FIGURE and hereinbeforedescribed. Through this method, the distortion of the rnetal in formingthe grooves and in deepening the grooves may be controlled so as toassure the formation of partitions shaped to engage the gas passage tube124 throughout its periphery.

Through the use of these method steps, the partitions 130 may befashioned to bridge a substantial annular space between the gas passagetube 124 and the intermediate shell or outer tube 110.

FIGURE 12 is illustrative of a modified method of forming the partitionsintegrally with the intermediate shell. In this form the grooves formedintegrally by distorting the metal inwardly are first collapsed to bringthe metal portions 136 and 138 of a groove into contiguous relation byendwise pressure exerted upon the intermediate shell 140 while theexterior regions of the tube adjacent the grooves are unconfined.

This action results in slight outward distortion of the metal at theregions indicated by the peripheral ridges 142 with the inner circularapices of the partitions 144 adjacent, but not yin -actual engagement,with the periphery of the gas passage tube 146. After the endwisecoliapsing of the tube or intermediate shell 140 is effected, matingcavity dies 150 of semicircular shape are moved transversely intoengagement with the ridges 142 to distort the metal of the ridgesinwardly, which action concomitantly moves the contiguous walls 136 and138 of each groove inwardly with the annular bight portion in 3engagement with the exterior peripheral surface of the gas passage tube146.

In this manner the integral partition is brought into engagement withthe gas passage tube and the exterior surface ridges of the intermediateshell are moved inwardly to present a smooth exterior cylindrical shapefor the intermediate shell or outer tube 140.

FIGURE 13 is illustrative of an intermediate shell, gas passage andsound attenuating unit wherein the transversely extending partitions 162are integrally formed with the perforated gas passage tube 164. In thisconstruction the grooves are formed from metal from the gas passage tube164 by forcing the metal of the tube outwardly through the use of agrooving roll such as that illustrated at 74 in FIGURE 3, the roll beingcarried by a member (not shown) projecting endwise interiorly of the gaspassage tube and movable transversely of the axis of the tube to forcethe metal outwardlyV to form the grooves.

The grooves in the tube 164 are preferably made of progressivelyincreasing depth from one end of Vthe tube to the other in the samemanner that the grooves formed by the method shown in FIGURE 3 are madeprogressively deeper. The outer tube or shell 160 may then be assembledwith the grooved gas passage tube 164- in the same manner that the gaspassage tube 48 is Iassembled with the intermediate shell 46 as shown inFIGURE 4.

The gas passage tube 164 may then be collapsed lengthwise in the samegeneral manner as illustrated in FIGURE 5, the endwise pressure exertedon the gas passage tube 164 collapsing the walls defining the out#wardly extending grooves in the tube 164 into contiguous relation andforcing them outwardly into engagement with the intermediate shell orouter tube 160 as shown in FIGURE 13. During the collapsing action onthe gas passage tube 164, a mandrel or other confining means may beinserted within the gas passage tube in order to assure the outwarddistortion of the metal at the regions of the grooves into engagementwith the intermediate shell or outer tube 160.

The adjacent partitions 162, shown in FIGURE 13, form high frequencysound attenuating chambers 166. It is preferable that the regions of thegas passage tube 164 at which the partitions 162 are formed beunperforated to provide partitions which are imperforate.

It will therefore be apparent that a sound attenuating unit particularlyconfigurated to provide high frequency sound Wave attenuating chambersmay be fashioned by forming transversely extending annularlyshapedintegral partitions, either from the metal of the -intermediate shell orouter tube or from the metal of the inner or gas'passage tube. Theopenings 50 in the gas passage tubes provide acoustic couplings with theadjacent sound attenuating chambers formed by the outer shell and thepartitions to attenuate or eradicate high frequency sound waves in astream of exhaust gases moving through the gas passage tube.

The sound attenuating unit of the invention is thus adaptable forpre-fabrication to facilitate rapid V:assembly of one or more units in amuffler construction. The partitions fashioned in accordance with thehereinabove described method may be spaced lengthwise at differentdistances so as to provide sound attenuating chambers of differentlengths as the grooves may be fashioned of the tube walls at anypositions along a tube. The construction provides separators orpartitions without the use of securing or welding individual components,rings or partitions between an intermediate shell and the gas passagetube.

It is apparent that, within the scope of the invention, modificationsand different arrangements may be made other than as herein disclosed,and the present disclosure is illustrative merely, the inventioncomprehending all variations thereof.

I claim:

1. The method of forming la telescoped tube assembly of two cylindricalmetal tubes of diierent diameters in concentric relation including thesteps of distorting metal of the wall of a first tube to formlongitudinally spaced circular grooves therein, arranging said firsttube in telescopic concentric relation with a second tube, andimpressing pressure lengthwise on said first tube to force the metaldefining the grooves to span the annular space between the tubes andinto the contiguous abutting relation and engaging the second tube.

2. The method Vof forming a -telescoped tube assembly of two cylindricalmetal tubes of diiferent diameters in concentric relation including thesteps of distorting metal of the wall of a lirst tube to formlongitudinally spaced circular grooves therein, arranging said firsttube in telescopic concentric relation with a second tube, andimpressing pressure lengthwise on said first tube to force the metaldefining the grooves laterally to span the `annular space between thetubes and into contiguous abutting relation and engage the circularridges provided by the grooves with the second tube.

3. The method of forming a combined gas passage means and soundattenuating unit including the steps of impressing lengthwise-spacedcircumferential groves in the wall of a first tubular metal member,arranging the rst tubular member in telescoping concentric relation witha second tubular metal member of substantially different diameter, andexerting pressure lengthwise on the irst tubular member to collapse thewall regions deining the grooves into contiguous abutting relation andto span the annular space between the tubular members and therebyestablish partitions and to engage the partitions with the secondtubular member forming sound attenuating chambers between the tubularmembers.

4. The method of forming a telescoped tube assembly including the stepsof distorting longitudinally spaced regions of metal of the wall of arst tube to form transversely extending circular grooves therein wherebythe grooves are of successively different depths, arranged said iirsttube in telescoping relation with a second tube of different diameterwith the axes of the tubes in substan tially coincident relation, andexerting pressure endwise on said irst tube to successively furtherdistort the metal defining the grooves into contiguous abutting relationand to span the annular space between the tubes and engage the circularridges formed by the grooves with the second tube.

5. The method of forming a telescoped tube unit including the steps ofrolling lengthwise spaced circumferential regions of a lirst metal tubeto form grooves therein, arranging the rst tube in telescoping relationwith a second metal tube of lesser diameter wherein the inner- 6. Themethod of forming a telescoped 4tube assembly including the steps ofdistorting metal of the wall of a irst tube to form transverselyextending, longitudinally spaced circular grooves therein, deepening thegrooves .to bring the wall regi-ons dening the grooves into closerrelation with successive grooves of increasing depth, arranging saidirst tube in telescopic relation with a second tube, and exertingpressure lengthwise of the iirst tube to further distort the metal intocontiguous abutting relation and to span the annular space between thetubes with the ridges provided by the grooves in engagement with thesecond tube.

7. The method of forming a combined gas passage tube and soundattenuating unit including the steps of impressing lengthwise-spacedcircumferential grooves of dilerent depths in the wall of a rst tubularmetal member, arranging a second tubular metal member of lesser diameterwithin and concentric with the first tubular member, and exertingpressure lengthwise on the first tubular member while confining theexterior surfaces of the rst tubular member at the regions of thegrooves to successively move the wall regions deiining the grooves intocontiguous abutting relation and to span the annular space between thetubes to thereby establish partitions and engage the partitions with thesecond tubular member forming sound attenuating chambers between thetubular members.

References Cited by the Examiner UNITED STATES PATENTS 567,328 9/1896Varman et al 153-73 743,193 11/1903 Rainforth 153-73 1,057,098 3/1913Smith 138-148 XR 1,602,550 10/ 1926 Pierce 153-73 1,878,424 9/ 1932Oldberg 181-48 2,047,442 7/ 1936 Starkweather et al. 181-48 2,147,0152/1939 Deremer 181-53 2,157,252 5/1939 Visser et al 153-73 2,264,524 12/1941 Hale. 2,401,606 6/ 1946 Brown 29-455 2,485,969 10/ 1949 Johnson153-73 2,680,901 6/ 1954 Kaiser 29-455 2,683,928 7/ 1954 Carson 29-5232,950,777 8/ 1960 Dermer 181-48 XR 2,958,389 11/1960 Dermer 181-543,092,896 6/ 1963 Stinehelfer 29-454 XR 3,104,735 9/1963 Ludlow et al.181-48 3,204,164 8/ 1965 Burke et al.

FOREIGN PATENTS 1,090,473 10/ 1960 Germany.

422,004 1/ 1935 Great Britain.

CHARLIE T. MOON, Primary Examiner. Liao sM1Low,wH1TMoRE A. wILTz,Examiners.

R. S. WARD, Assistant Examiner.

1. THE METHOD OF FORMING A TELESCOPED TUBE ASSEMBLY OF TWO CYLINDRICALMETAL TUBES OF DIFFERENT DIAMETERS IN CONCENTRIC RELATION INCLUDING THESTEPS OF DISTORTING METAL OF THE WALL OF A FIRST TUBE TO FORMLONGITUDINALLY SPACED CIRCULAR GROOVES THEREIN, ARRANGING SAID FIRSTTUBE IN TELESCOPIC CONCENTRIC RELATION WITH A SECOND TUBE, ANDIMPRESSING PRESSURE LENGTHWISE ON SAID FIRST TUBE TO FORCE THE METALDIFINING THE GROOVES TO SPAN THE ANNULAR SPACE BETWEEN THE TUBES ANDINTO THE CONTIGUOUS ABUTTING RELATION AND ENGAGING THE SECOND TUBE.